One type of electron gun recently proposed for color picture tubes is described in U.S. Pat. No. 3,995,194, issued to Blacker et al. This gun includes an electrode to which an operating voltage of approximately 12 kilovolts is applied. In the manufacture of tubes incorporating such guns, it is often desired to apply a "spot-knocking" voltage of approximately 30 kilovolts to this electrode in order to remove sharp points and particles therefrom which might otherwise later cause harmful arcing during tube operation. This spot-knocking voltage must be brought in through the base and stem of the tube, and severe voltage breakdown problems are encountered when conventional prior art bases are used.
U.S. Pat. No. 3,278,886 to Blumemberg et al discloses a type of wafer base in which a housing is disposed over the exhaust tubulation of an electron tube stem and the stem's lead-ins are disposed through apertures in a wafer flange extending from the housing. U.S. Pat. No. 3,979,157 to Dimattio discloses a modification of this type of wafer base in which the lead-ins are disposed in grooves in the housing wall of the base and lie against the floor of the grooves.
The Blumemberg et al base is especially designed for high voltage applications. To this end it incorporates a tubular silo structure which surrounds one of the lead-ins to which high voltage is applied, and a recess in the base into which a dielectric material is molded around the lead-ins. Both of these features serve to increase resistance against high voltage breakdown.
In mounting a base of the Blumemberg et al type to an electron tube stem, it has been the practice heretofore to simply insert a quantity of plastic dielectric material into the recess of the base and then apply the base to the stem. Since the dielectric material is applied to the base while it is out of contact with the stem, the result is a messy process. Alternatively, the plastic dielectric material may be injected through the exhaust tubulation housing. When the latter is done, sufficient material must be injected to completely fill the housing in order that some of the dielectric material is forced into the recess in the bottom of the base. The difficulty with this procedure is that exhaust tubulations are not of uniform volume from tube to tube, and hence the amount of dielectric material which must be injected varies from tube to tube. This prevents the injection of a specific amount of material and thus complicates the injection process.
Prior art bases such as the Blumemberg et al base experience another problem when they are used with neck-stem structures as conventionally fabricated in the color picture tube industry. In fabricating the neck-stem structure of a picture tube envelope, the neck is heated to soften the glass and fuse it to the stem. The heating is continued until a short length of neck section extending beyond the stem is completely severed from the remainder of the neck and drops free therefrom. When this short piece of neck section separates from the rest of the neck, it causes a drip or slight protuberance in the glass to form at one point around the periphery of the stem. When prior art bases have been applied to stems having drips of this type, the base is caused to tilt relative to the longitudinal axis of the tube. Such tilt, in addition to being aesthetically undesirable, often creates problems in inserting the base into its mating socket. Furthermore, the gap between the base and stem due to the tilting frequently allows the dielectric material injected into the base to flow therefrom leaving a deficiency of material to provide the desired dielectric body for high voltage breakdown insulation.